Class System

core/impl/main/java/org/directwebremoting/export/System.java:45–221

Various functions exported by DWR to help us with various book-keeping duties. @author Joe Walker [joe at getahead dot ltd dot uk]

 * @author Joe Walker [joe at getahead dot ltd dot uk]
 */
public class System
{
    /**
     * Generates and returns a new unique id suitable to use for the
     * CSRF session cookie. This method is itself exempted from CSRF checking.
     */
    public String generateId()
    {
        WebContext webContext = WebContextFactory.get();

        // If the current session already has a set DWRSESSIONID then we return that
        HttpServletRequest request = webContext.getHttpServletRequest();
        HttpSession sess = request.getSession(false);
        if (sess != null && sess.getAttribute(ATTRIBUTE_DWRSESSIONID) != null)
        {
            return (String) sess.getAttribute(ATTRIBUTE_DWRSESSIONID);
        }

        // Otherwise generate a fresh ID
        IdGenerator idGenerator = webContext.getContainer().getBean(IdGenerator.class);
        return idGenerator.generate();
    }

    /**
     * A method designed to be called on page load so the client knows about
     * the http and script sessions. This method doesn't actually do anything
     * however it does allow DWR's script session checking code to work
     */
    public void pageLoaded()
    {
    }

    /**
     * A method designed to be called when the client is offline.
     * When the server is back online this method will return immediately
     * so reverse AJAX polling may resume.
     */
    public void checkHeartbeat()
    {
    }

    /**
     * Call {@link ScriptSession#invalidate()} on the {@link ScriptSession}
     * that called this method.
     * Used by the page unloader.
     */
    public void pageUnloaded()
    {
        WebContext wctx = WebContextFactory.get();
        ScriptSession scriptSession = wctx.getScriptSession();

        log.debug("pageUnloaded is invalidating scriptSession: " + scriptSession);
        scriptSession.invalidate();
    }

    /**
     * Used by reverse ajax proxies to send data back to the server
     * @param key The unique id under which a callback is registered